In the industrial production of epichlorohydrin, a technology is mostly worldwide used, which comprises:                high temperature radical substitutive chlorination of propene to allyl chloride;        preparation of dichloropropanols by addition of hypochlorous acid to allyl chloride; and        dehydrochlorination of dichloropropanols with an alkali aqueous solution to epichlorohydrin.        
The basic features of this technology are, above all:                relatively mediocre total yield of the synthesis based on the starting propylene of ca. 73%;        low yield of the synthesis based on chlorine of ca. 38%;        high unit consumption of energy;        high unit volume of waste water of ca. 35 m3/t of epichlorohydrin, pollution AOX (Adsorbable Organic Halides), DIS (Dissolved Inorganic Salts) and COD (Chemical Oxygen Demand); and        use of hazardous propene and evaporated chlorine in the process.        
The technology of Showa-Denko (e.g., U.S. Pat. Nos. 5,011,980, 5,227,541 or 4,634,784), comprising:                palladium-catalyzed oxidation of propene with acetic acid to allyl acetate;        catex-catalyzed hydrolysis of allyl acetate to allyl alcohol;        catalytic chlorination of allyl alcohol to dichloropropanol; and        alkaline dehydrochlorination of dichloropropanol to epichlorohydrin is worldwide used to only minor extents.        
In both cases, the basic starting materials are propene, chlorine and an alkali, for example calcium hydroxide or sodium hydroxide.
Accordingly, for economic, environmental, and safety reasons, new synthetic routes are being sought worldwide. For several years, attempts have been made to manage a process of direct catalytic oxidation of allyl chloride to epichlorohydrin with hydrogen peroxide, or organic hydroperoxides, with use of catalysts based on titanium silicalites (e.g., U.S. Pat. Nos. 5,466,835, 6,187,935, 6,288,248, or 6,103,915) but without any commercial application to date.
One of further possible synthetic routes has been known since the beginning of the 20th century; its principle resides in catalytic hydrochlorination of glycerine by means of anhydrous hydrogen chloride according to the German patent to Boehringer, C. F. und Söhne, Waldhof b. Mannheim: Verfahren zur Darstellung von Mono- und Dichlorhydrin aus Glycerin und gasformiger Salzsäure, DE Patent No. 197308, 1906.
The principle is a reaction of glycerine with hydrogen chloride in the presence of carboxylic acids as catalysts, providing 1,3-dichloro-2-propanol and water. The said reaction is carried out in the liquid phase under temperatures of around 100° C. Pressure can be either atmospheric or elevated, for increasing the solubility of gaseous HCl in the reaction mixture. An optimal concentration of the homogeneous acetic acid catalyst is ca. 1-2% by weight; at higher concentrations undesired by-products are formed to a greater extent, which lower the yields. Besides acetic acid, the Patent mentions other carboxylic acids, propionic acid having been tested. The published yield of the batch arrangement without separation of water amounts to, in a control recalculation, ca. 75%. In order to increase the yield and reduce the hydrogen chloride loss a basic problem is removal of the water of reaction for shifting the equilibrium towards emerging dichloropropanol.
U.S. Pat. No. 2,144,612 has tried to solve the problem of sufficient removal of the reaction water at a suitable reaction temperature by the use of various kinds of inert, water immiscible solvents such di-n-butyl ether, ethylene dichloride, propylene dichloride or chlorobenzol, which allow to remove the reaction water as an acid distillate. The patent mentions that only the little amount of residues is formed, the reaction may be readily carried to completion, the solution of glycerol-dichlorohydrin obtained as a reaction product is substantially free from water and loss of glycerol-dichlorohydrin in hardly separable aqueous acid solution is minimized. Also the higher content of catalyst in range of 5% based on glycerine input is mentioned.
U.S. Pat. No. 2,198,600 has tried to solve the problem of the purification and the recovery of dichloropropanol from acid distillate by extraction using a suitable organic solvent for dichloropropanol, preferably di-n-butyl ether.
All the above mentioned methods described in the respective patents were developed as discontinuous batch processes.
In industrial scale such methods are not feasible for high losses of hydrogen chloride, the necessity of several batch reaction steps with long residence times of the order of hours to tens of hours, and hence high demands on the size of apparatuses, the logistics of raw materials and products, sanitation of waste streams, labour hygiene and the like. Also the use of significant portion of inert solvents required for the suitable results acceptable in the industrial scale significantly increases the reactor volumes and needs a lot of additional equipments for solvents handling, treatment, recovery etc.
For these reasons a method of continuous preparation of a mixture of 1,3-dichloro-2-propanol and/or 2,3-dichloro-1-propanol, characterized by high conversion of the starting materials, high yields of the products and high selectivity of the reaction system has been developed.